As a well-known technology for an indexable cutting insert that allows a cutting edge to be renewed by replacement or exchange of a cutting edge corner portion, there is known an insert in which a cutting tool material composed of one of cBN based sintered body, ceramics, and cermet (hereinafter, abbreviated as hard sintered body) is used for a surface involved in cutting (for instance, see PTL 1).
For a super hard cutting tool material composed of a hard sintered body, high precision shaping of raw material powder is difficult. Thus when the surface roughness of a machined surface is considered to be important, a method is adopted to improve a cutting edge geometry to be transferred to a workpiece by performing grinding after a flank face and a rake face are sintered.
Although the mainstream of cutting insert using the hard sintered body is that a small piece of cutting tool material composed of a hard sintered body is bonded to a corner portion of a base metal composed of cemented carbide, cermet or the like in consideration of cost effectiveness, some cutting inserts are composed of a hard sintered body in its entirety.
In a conventional product of cutting insert of this type, the entire rake face is ground in parallel with the insert bottom surface, and subsequently, a lateral face used as a flank face, a nose R portion, and a flank face are formed.
In the cutting insert including a surface involved in cutting, to which a hard sintered body is applied, when an object to be machined (workpiece) is a highly hard difficult-to-cut material such as a heat-resistant alloy or a hardened steel, chipping, fracture of a cutting edge is likely to occur due to inevitable vibration, impact in chip shearing, intermittent cutting, interrupted cutting. As reinforcement measures for a cutting edge, a negative land (chamfer, see also PTL 1) that blunts the cutting edge is provided along a cutting edge ridge line.
Also, depending on cutting application, a cutting insert is used in which the cutting edge ridge line portion has undergone honing treatment.
For cutting inserts for finish machining including a surface involved in cutting, to which a hard sintered body is applied, it is general that a great number of the cutting inserts is mounted on a planar grinder, and all of them are ground by a single grinding wheel so as to finish each cutting insert having the rake face at the same height as (flush with) the upper surface of the insert.
Such cutting inserts are disclosed in, for instance, PTL 2 cited below. Also, those cutting inserts are described in the catalogs disclosed on the Internet by tool manufacturers (for instance, Sumitomo Electric Hardmetal Corporation, Tungaloy Corporation, Mitsubishi Materials Corporation, Sandvik Company, and others).
For the type of insert in which a small piece of hard sintered body is bonded to a corner portion of the base metal, a method may be adopted in which the upper surface and bottom surface of the base metal are first ground, then the small piece of hard sintered body is bonded to the corner portion so that the upper surface of the small piece projects upward from the upper surface of the base metal, and subsequently, only the small piece is ground to form a rake face, and the lateral faces of the base metal and a nose R portion and a flank face to be provided in the small piece are finished.